Process for producing ethanol and for energy recovery

ABSTRACT

The present invention is directed to a process for the production of ethanol and energy. The process includes the steps of fermenting a corn mash in an aqueous medium to produce a beer. Next, the beer is distilled to produce ethanol and a whole stillage. The whole stillage is anaerobically digested to produce a biogas and a residue. The biogas is combusted to produce electricity and steam. The electricity and steam are used during the fermentation and distillation process. The residue may further be separated into a liquid fertilizer and top soil residue.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 11/561,996 filed Nov. 21, 2006 and U.S. patent application Ser.No. 11/845,821 filed Aug. 28, 2007, now U.S. Pat. No. 7,524,418, bothwhich claim priority to U.S. Provisional Application Ser. No. 60/751,792filed Dec. 19, 2005.

FIELD OF THE INVENTION

This invention relates to the production of ethanol and the conversionof ethanol production co-products (i.e., whole stillage, wet distillers'grain with solubles, and distillers dried grain with solubles) toenergy.

BACKGROUND

The dry mill production of ethanol is well known in the Prior Art. InFIG. 1, there is shown one exemplary illustration of such a process inaccordance to the prior art. First, corn 10 is mechanically grinded 15.The ground corn is mixed with water and enzymes in a steeping process 20which creates a “mash”. The mash is heated with yeast to promotefermentation 25 of the starches from the corn into ethanol. Thefermented mash is distilled 30 and the ethanol is extracted 40. The nowspent mash is dewatered and dried 35 to create distillers dried grainsand solubles (DDGS) 50. The DDGS 50 is then sold or consumed by animalsas feed stock.

The production of ethanol involves significant use of natural gas 45(35,000-40,000 BTU/gallon of ethanol produced) and approximately a thirdof the natural gas consumed in the current ethanol process is used inthe last step, to dry the mash to create a sellable product, DDGS.Moreover, the drying of the spent mash from the ethanol process tocreate the DDGS disadvantageously produces the emission of volatileorganic compounds (VOC) 55.

While ethanol has become part of the United States' strategy to developalternative fuels to eliminate reliance on oil and natural gas, there issignificant controversy over whether or not it takes more energy,currently non-renewable energy, to produce a gallon of ethanol than theenergy value of that gallon of ethanol. The most recent evaluation fromthe US Department of Agricultural concludes that ethanol has a positivenet energy value (i.e., ethanol energy content—energy required forethanol production); a significant increase in the net energy value forethanol would accelerate its acceptance as an alternative fuel and itsshare of the liquid fuels market.

In one prior art reference, U.S. Pat. No. 6,355,456 discloses a processof using wet grain residue from ethanol production to feed livestock.The manure collected from livestock is used for the production ofmethane. The '456 patent produces wet distiller's grains and solubles,(hereinafter “WDGS”) as a co-product of ethanol production. The WDGS ismixed with grain to produce cattle feed, which is fed to cattle inspecial barns with slatted floors in order to grow cattle and producemanure. The manure is placed into an anaerobic digester, where themanure is microbially converted to methane. The '456 patent furthermechanically separates solids and liquids in the sludge from the manure,dries the solids, and sells the digested liquid and dry solids. The '456further uses heat produced from the biogas combustion for dry millingthe grain.

While the '456 patent has some advantages, it also has somedisadvantages. For example, the livestock actually remove much of theenergy and ammonia that are present in the WDGS, which could berecovered and used. The WDGS is used to feed and grow the cattle, ratherthan try to convert the WDGS to energy. The present invention improvesupon the teachings of the '456 patent and provides for even greateradvantages over the '456 patent, discussed in detail below.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a new systemand process for ethanol production that further involves anaerobicdigestion of the whole stillage to convert it to biogas. The biogasgenerated is then used in place of natural gas in the ethanol productionas well as for the production of electricity.

The anaerobic digestion (biological conversion of organic compounds tobiogas or methane) of the whole stillage can generate more methane thanthe natural gas used in production of the ethanol. The excess methanecan produce approximately 75% of the electricity required for ethanolproduction. The present invention has the potential for increasing thenet energy value for ethanol by 9.6 times, significantly reducing thereliance of the ethanol industry on natural gas, and significantlyreducing the financial exposure of the ethanol industry to twocommodities with volatile pricing, natural gas and distiller's driedgrains and solubles (DDGS). The invention further allows for theproduction of ammonia fertilizer from the whole stillage. Whole stillagecontains approximately 20% protein, which is high in nitrogen. Theanaerobic digestion process releases the nitrogen into the water asammonia. The ammonia in the water can be recovered and used forfertilizer.

In one embodiment of the present invention, a process of producingethanol is provided. The process includes grounding corn to produce adry grind. The dry grind is mixed or soaked with water during a steepingprocess. Enzymes and yeast are added and then the mixture is fermented.After fermentation a beer is created which is distilled in order toextract ethanol.

It should be known that the actual processes of steeping, fermentationand distillation are well known in the industry and may include otheradditives or steps not disclosed herein, but would be included forproper processing of the corn to ethanol.

The ethanol is extracted from the beer leaving whole stillage. The wholestillage, anaerobic digester sludge, and recycled water are mechanicallymixed together to create the mixed liquor in a slurry tank. The mixedliquor is pumped from the slurry tank to an anaerobic digester. Theanaerobic digester is a continuous flow biological reactor which iseither plug flow or completely mixed. The mixed liquor is mixed in thedigester either mechanically or by sparging with biogas. The anaerobicdigester is heated using heat from the combustion of biogas. The biogasis collected from the headspace of the anaerobic digester and used for:fuel in an internal combustion engine to produce electricity and fuelfor a boiler to produce steam. The electricity produced is used to powermechanical systems in the ethanol production facility and the anaerobicdigester system. The steam produced in the boiler is used in theproduction of ethanol. Waste heat is collected from the coolant of theinternal combustion engine and the exhaust gas of the internalcombustion engine using a fresh water system. The fresh water system isused to heat the anaerobic digester. After being in the anaerobicdigester the mixed liquor is pumped from the digester to a screw pressfor separation of the digested solids from the digested liquid. Thedigested solids are dewatered and then sold as a soil amendment. Thedigested liquid is pumped into an air stripping tower for removal of theammonia. The water following ammonia removal is recycled back to theslurry tank. The off-gas from the ammonia stripping tower goes into anammonia recovery scrubber where the ammonia is recovered at a highconcentration in water. The concentrated ammonia solution is then soldas fertilizer.

The invention advantageously will reduce VOC emissions from ethanolfacilities by eliminating the source of the VOC (i.e., drying the wholestillage) and will reduce greenhouse gas emissions by creating theenergy necessary for ethanol production from a renewable source (i.e.,corn). The methane generated from anaerobically digested whole stillagecame from carbon dioxide in the atmosphere through the growth of thecorn plant. The invention will eliminate the need for natural gas in theethanol production process and will reduce the electrical requirement by75%. The energy reduction is achieved because natural gas is producedinternally in the process through anaerobic digestion and electricity isalso produced internally to the process.

The present invention has many advantages and differences over the '456patent including: the use of whole stillage from the ethanol productionprocess rather than the WDGS used in the '456 patent; the '456 patentmixes WDGS with grain to produce cattle feed, the present invention doesnot produce cattle feed; the '456 patent feeds cattle in special barnswith slatted floors in order to grow cattle and produce manure, thepresent invention does not need cattle or special barns and does notproduce manure as an intermediate product; the '456 patent puts manureinto an anaerobic digester and microbially converts the manure tomethane, the present invention creates a mixture of whole stillage,recycled anaerobic sludge, and recycled water to create a mixed liquorto be anaerobically digested to methane; the '456 patent mechanicallyseparates the solids in the sludge from the liquid, dries the solids,and sells the digested liquid and dry solids, the present inventionmechanically separates the solids from the digested mixed liquor, sellsthe solids without drying, recovers the ammonia in a concentrated liquidusing air stripping and air scrubbing, and recycles the recovered water;and the '456 uses the heat produced from biogas combustion for drymilling grain, the present invention uses the heat from combustion ofthe biogas to produce electricity for ethanol production, steam forethanol production, and recovers waste heat from electricity productionto heat the anaerobic digester.

In one embodiment of the present invention an integrated continuousprocess for the production of ethanol and energy is provided. Theprocess includes fermenting a corn mash in an aqueous medium to producea beer. The beer is distilled to produce ethanol and a whole stillage.The whole stillage is mixed with water and bacteria and thenanaerobically digested which produces a biogas and a residue. The biogasis combusted to produce electricity and steam. The electricity and steamis utilized for the fermentation and distillation of the ethanol.

The process may also include dehydrating the distilled ethanol toproduce an ethanol with a higher proof then the aforementioned distilledethanol, During the dehydrating step water is recovered and utilizedduring the distillation step.

The process may also separate the residue into digested liquids anddigested sludge. The digested sludge is dewatered to produce a soilamendment and a residual water that is recycled into the whole stillage.The digested liquid may also be stripped of water and scrubbed toproduce an ammonia solution.

BRIEF DESCRIPTION OF THE DRAWINGS

A fuller understanding of the foregoing may be had by reference to theaccompanying drawings, wherein:

FIG. 1 illustrates a current ethanol production process known in theprior art;

FIG. 2 illustrates a process of producing ethanol in accordance to anembodiment of the present invention;

FIG. 3 illustrates a 3,000 head dairy anaerobic digester system inaccordance to an embodiment of the present invention;

FIG. 4 illustrates a 5,000 head dairy and ethanol plant anaerobicdigester system in accordance with an embodiment of the presentinvention; and

FIG. 5 illustrates a corn grower, ethanol producer and dairy farmersystem in accordance with an embodiment of the present invention;

FIG. 6 illustrates a dry milling process for ethanol production withself generation of energy in accordance with an embodiment of thepresent invention;

FIG. 7 is a schematic process flow diagram of a pilot scale anaerobicdigester recovery system in accordance with an embodiment of the presentinvention;

FIG. 8 is a top plan view of the anaerobic digester illustrated at FIG.7; and

FIG. 9 is a sectional view of the anaerobic digester illustrated at FIG.7.

DESCRIPTION OF THE INVENTION

Referring now to FIG. 2, there is shown and disclosed one embodiment ofthe present invention, which illustrates a process for the production ofethanol. In this first system 100, corn 102 is grounded 105 into a drygrind. The dry grind then undergoes a steeping process 110 where waterand enzymes are added to produce a mash. The mash is then fermented withyeast, 115. The fermentation is then distilled 120, to extract ethanol125. The spent mash or remainder goes into an anaerobic digester 130which extracts ammonia fertilizer 135, top soil 140 and biogas 150. Thebiogas 150 is used to help power an electrical generator 155 and a steamgenerator 160 which is used in the system 100. The ammonia fertilizer135 and top soil 140 may be sold and/or consumed on premise. In thisfirst system, the DDGS or WDGS is not consumed by animals, rather thewhole stillage is feed into the anaerobic digester 130 to extract thefull amount of energy in the whole stillage.

The Development and Use of Biomass for Energy Production.

Biomass can be converted to energy in several ways. Burning plantmaterial, such as sawdust, is one method for conversion of biomass toenergy. Collection and combustion of landfill gas is another. Many plantand animal tissues, including manure, can also be converted to methaneby anaerobic microbial activity and the biogas produced (i.e., a mixtureof methane and carbon dioxide) can be used as a fuel. It is throughanaerobic microbial conversion to methane that many agricultural (e.g.,manure) and agri-industry (e.g., distiller's grains and solubles)byproducts can be converted to fuel while leaving odorless organicmatter and nutrients (i.e., ammonia nitrogen and phosphate) availablefor amendments to cropland.

In parallel with the energy sector promoting the development ofrenewable energy sources, the livestock industry is coming underincreasing regulatory pressure to reduce the environmental impacts ofconcentrated animal feeding operations (CAFOs). The impacts of CAFOs onthe environment focus on the management and disposal of manure. Theseimpacts include airborne emissions of odorous organic compounds,hydrogen sulfide, and ammonia, release of raw liquid manure into waterbodies (surface and groundwater), and the over application of phosphoruson fields due to manure application based on nitrogen content. The CAFOmanure is a biomass energy source because of its methane generationpotential through the use of anaerobic microorganisms. Anaerobicdigestion of manure produces methane gas (i.e., natural gas) from thisrenewable energy source. In addition, anaerobic digestion of the manurewill convert organic nitrogen to ammonia, cause precipitation ofphosphorus as struvite, and eliminate volatile organic compounds thatproduce offensive odors. Thus, anaerobic digestion of manure reducesmany of the CAFO impacts while producing renewable energy.

The following sections present an example of how distributed, renewableenergy (on-farm anaerobic digestion of manure) can cost effectively meetmany of the environmental challenges of CAFOs. In addition, a secondexample will be presented to show how a CAFO (e.g., large dairy) couldbe teamed with an energy intensive Industry (e.g., ethanol productionfacility) to symbiotically use co-products and nutrients for theproduction of natural gas, electricity, ethanol, and milk.

Anaerobic Microbial Conversion

Anaerobic microbes are capable of generating energy from the oxidationof organic molecules without the use of oxygen. These organisms canreduce nitrate, sulfate, and carbon dioxide while oxidizing complexorganic molecules. The products of anaerobic microbial metabolism arenitrogen gas, hydrogen sulfide, and, in the largest quantity, methane.

Anaerobic conversion of organic matter to methane occurs in a series ofsteps that are accomplished by different groups of organisms. The firststep in the anaerobic process is hydrolysis. In this step complexorganic polymers (i.e., starch, triglycerides, and proteins) are reducedto their monomers (i.e., glucose, fatty acids, and amino acids). Thesecond step oxidizes these monomers to 3-5 carbon organic acids (i.e.,propionic, butyric, and valeric acid). The third step converts theseacids to acetic acid. The final step takes acetic acid, as well ascarbon dioxide produced in earlier reactions, and converts them tomethane. It should be noted that amino acids contain nitrogen. Throughthe anaerobic conversion of amino acids to methane, the nitrogen fromthe amino acids is released from the molecule as ammonia. Therefore, theanaerobic microbial activity also releases ammonia nitrogen from itsorganically bound state in the amino acid, making it more available forplant uptake.

The methane production from protein, starch, and fat can be approximatedusing microbial stoichiometry, a well known process. Based on theoverall chemical reactions for methane production from these complexorganic molecules, the methane generation capacities for each generalgroup of molecules have been calculated (Table 1). The potentialelectricity that could be generated from the methane produced throughanaerobic conversion was also calculated assuming a 25 percent efficientgenerator.

TABLE 1 METHANE PRODUCTION AND ELECTRICAL POWER GENERATION FROM COMPLEXORGANIC MOLECULES AND MANURE Methane Generation Electricity GeneratedMolecule (ft3/lb) (kW-hr/lb) Protein 4.5 0.33 Carbohydrate 3.0 0.22 Fat15.1 1.11 Manure (volatile solids) 6.1 0.45

Anaerobic Digester System

The conversion of organic molecules to methane by anaerobic microbesmust occur in an environment void of oxygen. The rate of conversion willbe proportional to the temperature of the environment and the number ofmicrobes in the system.

Referring now back to the figures, FIG. 3 presents a system 200 capableof converting dairy manure to methane gas. The system 200 would requiremaintaining the manure in an oxygen-free environment at approximately100° F. for 15 to 20 days. Manure is scraped 205 from the stalls and themilking parlor wash water 210 are mixed together into a reception pit215 creating a slurry. The slurry of approximately 8 percent solids ispumped into the concrete heated digester 220 for 15 to 20 days. Theeffluent from the digester 220 is then moved into a collection sump 225where it is then mechanically dewatered by a screw press 230 or similarseparator (such as a centrifuge) with the solids being used for animalbedding 235 and the liquid used for fertilizer 240. Biogas 245 from thedigester 220 can be used by a generator 250 to produce electricity 255and hot water 260, which can be used for the milking parlor wash water210 and by the digester 220.

A process flow diagram for the combined digestion of manure anddistillers grains and solubles (DGS; ethanol plant byproduct) system 400is presented in FIG. 4. The scraped manure 405, milking parlor washwater 415 and DGS 410 is added to a slurry tank 420 along with recycledwater, if necessary. The recycled water would be used to ensure theinfluent to the anaerobic digester is between 10 percent and 15 percentsolids content. The slurry is then pumped into a heated concrete plugflow anaerobic biological reactor or digester 425. The reactor is mixed,perpendicular to the axis of flow to prevent vertical stratificationwithin the reactor while maintaining the plug flow. Biogas 430 iscollected in the reactor headspace. After 15 to 20 days in the reactorthe effluent slurry is moved to a collection sump 435 and ismechanically dewatered by a screw press 440. The solids are availablefor dairy bedding 445 or an organic soil amendment and the liquid can berecycled 450 into the slurry tank 420 and/or a liquid fertilizer 455.Thus the manure and DGS is converted to fuel (i.e., methane gas),fertilizer (i.e., ammonia in the separated liquid) and animal bedding ortopsoil (i.e., the digested solids will have the properties of topsoil).The biogas 430 is used by a generator 460 to convert the same toelectricity and hot water. The reactor is heated using a portion ofmethane gas generated either through a boiler or from the waste heatproduced by an electrical generator. The electricity can be used to runthe ethanol facility 465 which produces the DGS.

3,000-Head Dairy Example

As an example, consider a 3,000-head dairy (scrape manure collection)which produces approximately 60,000 gallons per day of liquid manure at8 percent total solids (includes milking parlor wash water). Manuresolids are approximately 86 percent volatile. Based on the informationpresented above, the methane generated from the manure is calculated at219,600 ft³ methane/day. This would equate to 220 mmBTU/day of naturalgas or 16,100 kW-hr/day of electrical power (25 percent generationefficiency). Waste heat recovery from electrical power generation couldalso provide 60 mmBTU/day. A 1,400 lb. lactating dairy cow producesabout 0.57 lb/day of nitrogen in its manure. This equates to 0.86tons/day of nitrogen, which is equivalent to 1.1 tons/day of anhydrousammonia fertilizer. The non-digested fiber in the anaerobic digestereffluent will be approximately 15 lbs/day/cow. Half of the dewatered/airdried solids will be used for bedding. The remainder of the dried solidsare sold.

An anaerobic digester with 650 kW of electrical generating capacityservicing the 3,000 head dairy would cost approximately $2,700,000.Electricity is sold to the local utility for $0.06/kW-hr. The stateprovides a $0.015/kW-hr renewable energy production incentive. Excessbedding is sold for $15/ton. Operation and maintenance of the digesterand generators was estimated at $0.02/kW-hr. It is also assumed that thecost of the digester and generators are depreciated over a 10-yearperiod and that the system owner can take full advantage of thedepreciation loss. Based on these assumptions, a private investor couldbuild, own, and operate an anaerobic digester based power generationsystem on a dairy farm and receive a return on investment (ROI) inexcess of 12 percent.

Corn Grower-Ethanol Plant-Dairy Farm System

An approach to improving the energy efficiency of the biogas is toco-locate the anaerobic digester with a natural gas intensive process.In this example, a 50 million gallon per year ethanol productionfacility with an anaerobic digester is co-located with a 5,000-headdairy farm in a corn growing region. FIG. 5 presents the symbioticrelationship between the corn grower, ethanol producer, and dairyfarmer.

As illustrated in FIG. 5, system 500 includes 128,000 acres of land 505in the vicinity, 8-10 mile radius, of the ethanol facility 510. The land505 is needed for growing 19.2 million bushels of corn. 18 millionbushels 508 are used by an ethanol facility 510 to produce 50 milliongallons of ethanol 512. 1.2 million bushels 514 are fed directly to theanaerobic digester 515 for additional energy production. 18,250 tons peryear of wet distillers grains and solubles (WDGS) 517 are produced bythe ethanol facility 510 and are consumed by the 5,000 dairy cows 520.127,750 tons per year of WDGS 522 (produced by the ethanol facility 510)are sent directly to the anaerobic digester 515 for energy production.The 5,000 head of dairy cattle 520 produce 1 million hundred weight(cwt) of milk per year 525, which is bottled and sold, and produce 63.9million gallons of liquid manure 527, which are sent annually to theanaerobic digester 515 for energy production.

The digester 515 produces 2.18 million mmBTU per year of biogas. 1.33million mmBTU of the biogas 530 is used directly to produce steam forethanol production. 0.85 million mmBTU are converted to electricity 532for use in ethanol production. 13,600 tons of dried digested solids areproduced each year by the anaerobic digester 535. 6,800 tons of thedried digested solids are used for bedding 540 at the diary farm, while6,800 tons of the dried digested solids are sold 545 each year. Thedigested liquids contain 6,340 tons per year of ammonia nitrogen 550that will be applied to the fields to support corn growth. An additional4,200 tons per year of anhydrous ammonia 555 will be purchased in orderto meet the growth requirements of the corn.

Therefore, with the addition of 4,200 tons per year of anhydrous ammoniaand seed corn for 128,000 acres, this theoretical system could annuallyproduce 50 million gallons of ethanol, 1 million cwt of milk, and 6,800tons of bedding/compost.

This approach provides many environmental benefits to the ethanolfacility and the dairy farmer. The ethanol facility does not need to drythe distillers grains and solubles thus eliminating ⅓ of their naturalgas use, significantly reducing volatile organic compound (VOC)emissions, and eliminating the need for a thermal oxidation unit formanaging VOC emissions. Odorous emissions from raw manure storage at thediary are significantly reduced because all manure is digested prior tostorage eliminating noxious VOCs in the manure. The stored digestedliquid will have significantly less biochemical oxygen demand thusreducing its potential effects on a receiving body of water should anaccidental release occur. Finally, anaerobic digestion promotesprecipitation of phosphorus such that the digested liquid will havesignificantly less phosphorus than raw manure. This will reduce thephosphorus load on fields when digested manure is applied at agronomicrates for nitrogen.

Assuming an existing dairy with neighboring corn farmers, the ethanolplant and digester could be constructed for approximately $80 million.Table 2 provides a theoretical annual balance sheet for the operation.It was assumed that ethanol is sold for $1.20/gal and milk is sold at$13.50/cwt.

TABLE 2 Annual Balance Sheet for Corn/Ethanol/Dairy System CategoryAnnual Debit/Credit ($ million) Fertilizer (1.47) Seed Corn (5.12)Ethanol Facility O&M (18.0) Dairy Farm O&M (8.65) Corn Farm O&M (8.53)Ethanol Sales 60.0 Milk Sales 13.5 Bedding Sales 0.10 Ethanol ProductiveIncentive 3.0 Renewable Electricity Production 0.82 Incentive Annual NetRevenue 35.65

Based on $35.65 million in annual revenue, corn growers would be paid aneffective price of $2.10/bu for corn and the dairy farm would be paid aneffective price of $14.45 cwt for milk. After these payments are made,the ethanol plant investors would receive approximately million inprofit. Assuming that the ethanol plant and digester are depreciatedover 10 years, the ethanol plant investors would receive a minimum of 12percent ROI. Thus, Anaerobic digestion can address many of the criticalenvironmental issues facing CAFOs. Using a renewable energy approach,anaerobic digestion with electricity production on large dairy farms canbe an attractive investment for a private investor interested indeveloping renewable energy. Further, bundling of agri-industry entitiesallowing for renewable energy production as well as raw materialproduction and by-production utilization (i.e., corn production, ethanolproduction, and milk production) provides for the production of milk andethanol with very little input of fossil fuels (fossil fuel input onlythrough the production of the additional anhydrous ammonia purchased forcorn production). This bundled system is not only an attractiveinvestment, it also produces ethanol with a significantly reduced energyinput and it provides control of volatile commodity prices (e.g., corn,natural gas, and DDGS) allowing the bundled organization to bettermanage its financial risk.

Referring to FIG. 6, there is shown and disclosed one embodiment of thepresent invention, illustrating a system 600 that includes a process forthe production of ethanol 602 and a process of self-generating energy604. The process of producing ethanol 602 begins with whole corn 605that is ground 610 to create a corn meal 615. The corn meal 615 is mixedwith water 620 and enzymes 625 to create a mash 630. The mixing processis typically referred to as a steeping process. The mash 630 is mixedwith yeast 635 and enzymes 640 and then fermented 645 to create a beer650. During the fermentation process 645 carbon dioxide may be recovered635. The beer 650 is then distilled 660 to create a 190 proof ethanol665. The 190 proof ethanol is further dehydrated 670 to create a 200proof ethanol 675 that is sold. During the dehydration process 670, anyrecovered water 680 is cycled back to the distillation process 660.

When the 190 proof ethanol is extracted during the distillation process660, whole stillage 685 remains and is moved to a slurry tank 690 forthe self generation of energy process 604. The whole stillage 690 ismechanically mixed with recycled water 692 and 694 and recycled bacteria696 to create a mixed liquor 698. The mixed liquor 698, which is between10% and 15% solids concentration is moved or pumped to the anaerobicdigester 700.

The anaerobic digester 700 is a continuous flow biological reactor whichis either plug flow or completely mixed. The mixed liquor is mixed inthe digester either mechanically or by sparging with biogas. Theanaerobic digester is heated to between 90° F. and 110° F. using heatfrom the combustion of biogas. The biogas 705 is collected from theheadspace of the anaerobic digester 700 and used for: fuel in aninternal combustion engine to produce electricity 710 and fuel for aboiler 715 to produce steam. The electricity produced is used to powermechanical systems in the ethanol production process 602 and the energygeneration process 604. The steam produced in the boiler 715 is used inthe production of ethanol. Waste heat is collected from the coolant ofthe internal combustion engine and the exhaust gas of the internalcombustion engine using a fresh water system. The fresh water system isused to heat the anaerobic digester.

After being in the anaerobic digester 700 for 10 to 20 days, the mixedliquor 720 is pumped from the digester to solids separator 725, whichmay be a screw press. During the separation process digested solids orsludge 730 is separated from the digested liquid 735.

Bacteria 696 from the sludge 730 is recycled to the slurry tank 690,while the remaining sludge is sent to a dewatering process 740. Duringthe dewatering process 740 any water is recycled 694 back to the slurrytank. The remaining solids are then sold as a sold amendment 745.

The digested liquid 735 is pumped into an ammonia stripper 750 forremoval of the ammonia. The water 692 following ammonia removal isrecycled back to the slurry tank 690. The off-gas 755 from the ammoniastripping tower goes into an ammonia recovery scrubber 760 where theammonia is recovered at a high concentration in water. The concentratedammonia solution 765 is then sold as fertilizer.

In another embodiment of the present invention, shown in FIG. 7, it isdesirable to provide an ethanol facility that is able to self-generateall of its own energy. This will be accomplished through the anaerobicmicrobial conversion of the whole stillage (ethanol productionbyproduct) to methane, ammonia, and stable (non odorous) organiccompost. The present invention will entail the alternative processing ofwhole stillage into energy ammonia fertilizer and an organic soilamendment and not into an animal feed. Laboratory results suggest that11.6 million BTUs of methane can be produced per dry ton of wholestillage anaerobically digested. In addition, 85 lbs. of ammonianitrogen is produced per dry ton of whole stillage digested. Using anatural gas price of $8/mmBTU, a DDGS price of $65/ton, an estimatedcapital cost for a digester to service a 50,000,000 gallon per yearfacility at $25 million, and an annual operating cost of $500,000, theinternal rate of return (unleveraged) is greater than 20%.

The present invention has four objectives that address the questionsnecessary to validate the economic viability of the concept of producingall of the energy for ethanol production from anaerobic digestion of thewhole stillage.

First, to determine the conversion of whole stillage to methane andcarbon dioxide as a function of the hydraulic retention time.Technically DDGS can be anaerobcially converted to methane. The actualconversion must be determined because the economic viability relies onthe heat value of the methane generated per ton of DDGS digested. Therate of conversion will dictate the size of the digester required andthus have a marked effect on the project capital cost.

Second, to determine biogas quality, treatment requirements for use ofthe biogas, and appropriate biogas treatment technologies to achieve thedesired gas quality. Biogas is a mixture of methane and carbon dioxide.The ratio of methane to carbon dioxide will determine the heat contentof the gas and thus its monetary value. Biogas can also contain ammoniaand hydrogen sulfide. The combustion of ammonia and hydrogen sulfide canadd to nitrogen and sulfur air emissions as well as causing theproduction of acids in the combustion chamber. Thus, evaluating biogasquality and the best available technology for the removal of ammonia andhydrogen sulfide will be critical for evaluating the economics of thisconcept.

Third, to determine the digested biomass consistency and appropriatetechnologies for dewatering. The anaerobically digested solids can beused in applications as top soil. The economic viability of the sale ofthese solids will depend on technology required to dewater them.Therefore, it will be important to determine the consistency of thedigested solids (i.e., particle size distribution and water retention)in order to evaluate cost effective dewatering technologies.

Fourth, to determine appropriate technologies for ammonia recovery.Since DDGS is 29% protein, a significant amount of ammonia will beproduced from the anaerobic digestion of the DDGS. The ammoniaconcentration must be managed in the anaerobic digester or it willinhibit the production of methane. The ammonia also has high marketvalue as a fertilizer. Therefore, recovery of the ammonia is technicallynecessary and it will also provide additional revenue. The bestavailable technology for ammonia recovery from digested liquid must bedetermined.

The first phase in implementation will include the design andconstruction of the energy generation system 604, illustrated in FIG. 7.The system 604 will consist of 2-1,000 gallon cylindrical anaerobicdigester tanks 700 (also shown in FIGS. 8 and 9). Each tank 700 includesan interior support pipe 800 and a plurality of partitions 804 extendingradially outwardly from the support pipe 800. The partitions 806 areheld in place by support clips 806 positioned on the outer tank wall 807and on the interior support pipe 800. Preferably, there are sixpartitions 804 that separate the each tank into six sectors 802 tocreate six complete mix digesters in series within each tank.

To facilitate the biogas sparge mixing within the tank, each sector 802includes coarse bubble aerators 808 near the bottom of the tank withbiogas pipes 810 running upwardly along the interior support pipe 800.In addition, to heat and maintain the temperature of the mixed liquor inthe tank heat exchange pipes 812 are provided with inflow pipes 814 andoutflow pipes 816. Lastly, the tanks 700 may be provided with under flow818 and over flow 820 windows.

Referring back to FIG. 7, the system 604 feeds the tanks 700 from theslurry tank 690. A slurry tank transfer pump 830 may be employed to helpdirect and control the amount off mixed liquor entering the tank. Thewhole stillage will enter the slurry tank 690 from the ethanolproduction process 602.

As mentioned the temperature of the tanks 700 is maintained andcontrolled by hot water. The water moves in and out of the tank by pipes814 and 816. The water is first heated in water heaters 832. The heaters832 will typically include a pressure relief valve 834 and a hot waterexpansion tank 836, because during heating of the water, the water willtypically expand. Without the expansion tank 836, the pressure insidethe inflow pipes 814 may become too strong and create shock waves orknocking. The water exiting the tank 816 is cycled back to the waterheaters.

From the tank 700, the mixed liquor will be pumped 840 into the soldseparator 724 or a screw press. The solids are stored and sold as soilamendment while the liquid 735 is moved into a holding tank 845 for therecovery of ammonia. A pump 850 is used to move the liquid 735 from theholding tank 845 to the ammonia recovery system 855. During the ammoniarecovery, water is recovered or removed and possibly sent to a sewer860.

The biogas is collected in the header or the tank and sent to thegenerators. Throttle valves 865 are used to control the flow of thebiogas from the tanks 700.

During initial startup of the system 604, the digester 700 will consistof seeding and acclimatization. The digester will be seeded with amixture of anaerobic sludge, raw manure, and whole stillage. Potablewater will be added to create the mixed liquor with a solids content of15%. Both digesters 700 will be filled with this mixed liquor andbrought up to 100° F. using the hot water system. Once biogas productionbegins, biogas sparging will be initiated for mixing. The quantity andquality of biogas will be monitored continuously. Daily feed to thedigesters 700 will be periodically increased slowly reducing thehydraulic retention time. Acclimatization will be complete when thedigesters can receive 50 gallons of feed per day and have operated inthis mode for one solids retention time (i.e., 20 days).

Digester 700 testing will commence once both digesters are acclimatized.Digester 1 will operate at 20 day solids retention for the remainder ofthe pilot scale study. The effluent from Digester 1 will be used toevaluate digested solids dewatering technologies and ammonia recoverytechnologies. The system will be equipped with a screw press which hasbeen very effective for solids separation in manure anaerobic digestionsystems. Several other technologies may also be used to determine theability to remove and dewater digested solids, which may include VSEP(vibratory assisted membrane filtration), centrifuges or filter press.In parallel with the solids dewatering evaluation, ammonia recoverytechnologies will also be evaluated. The system will have the AmmEL-HCsystem (ENPAR Technologies, Inc.), modified for ammonia recovery,installed. Recovery of ammonia using nanofiltration or reverse osmosismay also be used.

Digester 2 will be used to determine the effects of hydraulic retentiontime (HRT) on conversion of whole stillage to methane. Onceacclimatization is complete, the volume of feed batch fed daily to thedigester will be increased to reduce the HRT in 1-day incrementsDigester 2 will operate at each new HRT for one HRT or until the dailymethane generation rate is stable, which ever takes longer. The one daydecreases in HRT will continue until the digester is operating at a 10days HRT. This evaluation is expected to take up to 8 months.

Anaerobic digestion of whole stillage for self-generation of energy foran ethanol facility has three major benefits: increased energyefficiency, reduced financial risk, and support of sustainableagriculture. As mentioned above, anaerobic digestion of whole stillagehas the potential of producing as much as 11.6 mmBTU per dry ton ofwhole stillage. This is more than sufficient energy to produce the steamand 75% of the electricity used to produce that ton of stillage. Therecovery of 85 lbs. of ammonia nitrogen per dry ton of whole stillage isapproximately 60% of the nitrogen fertilizer necessary for grow the cornin that ton of whole stillage. It is predicted that the anaerobicconversion of whole stillage to energy will increase the net energyvalue of a gallon of ethanol from 5,880 BTUs (USDA value) to 56,860BTUs. Thus, anaerobic digestion of whole stillage represents asignificant increase in the overall energy efficiency of the dry millingethanol process.

The current financial model for an ethanol plant is plagued by the pricevolatility of four commodities: corn, DDGS, natural gas, and ethanol. Byusing the whole stillage to produce 89% of the energy for an ethanolfacility, two volatile commodities are removed from the financial modelreducing the financial risk for the production facility. It should notedthat eliminating natural gas from the production process will have avery significant effect on the financial performance of ethanolfacilities because of the current increasing trend in natural gasprices.

Historically, nutrient recovery from manure or agra-industry wastes haslead to over application of phosphorus because the nitrogen tophosphorus ratio in these wastes is not appropriate for agriculture. Theanaerobic digestion of whole stillage with ammonia recovery will allowfor the use of nitrogen as a fertilizer without any phosphorus. Themajority of the phosphorus contained in the whole stillage will beprecipitated in the anaerobic digester. The phosphorus will be part ofthe dewatered solids and will not be associated with the ammonia. Thus,anaerobic digestion allows for nutrient waste recovery without thedetrimental effects of over application of phosphorus.

From the foregoing and as mentioned above, it is observed that numerousvariations and modifications may be effected without departing from thespirit and scope of the novel concept of the invention. It is to beunderstood that no limitation with respect to the embodimentsillustrated herein is intended or should be inferred.

1. An integrated continuous process for the production of ethanol andself generating energy on a commercial scale after an initial processstart-up, said integrated continuous process comprising the steps of:(a) fermenting a mash in an aqueous medium to produce a beer; (b)distilling said beer to produce commercial scale quantities of ethanoland a remainder; (c) digesting a mixture containing said remainderanaerobically in a digester tank to produce commercial scale quantitiesof a biogas and a residue; (d) combusting said biogas to produceelectricity and steam; (e) utilizing steam produced by said the ifcombustion during the steps of fermenting and distilling to produce saidethanol; and (f) utilizing electricity produced by said combustionduring the step of fermenting the mash; said commercial scale of biogasbeing defined to include up to 11.6 million BTUs of methane per dry tonof said remainder anaerobically digested with the steam produced by step(d) being sufficient to provide, after said initial start up of saidintegrated continuous process, all the steam of step (e) used to producesaid ethanol and said remainder of step (b).
 2. The process of claim 1wherein said remainder is a stillage or a slurry.
 3. The process ofclaim 2 wherein said stillage or slurry is approximately 8 to 15 percentsolids.
 4. The process of claim 1 wherein said digester tank includes aplurality of sectors to create a series of mixing digesters.
 5. Theprocess of claim 1 further comprising: dehydrating the distilled ethanolto produce an ethanol with a higher proof than said distilled ethanol,wherein during the dehydrating step water is recovered.
 6. The processof claim 1 further comprising mixing the remainder with bacteria andwater prior to digesting.
 7. The process of claim 1 further comprisingthe steps: separating the residue from the digestion step into digestedliquid and digested sludge.
 8. The process of claim 7 further comprisingthe step: dewatering the digested sludge to produce a soil amendment anda water residue.
 9. The process of claim 8 further comprising the step:recycling said water residue from the dewatering of the digested sludgeinto the remainder.
 10. The process of claim 7 further comprising thestep of recovering of ammonia from the digested liquid.
 11. The processof claim 10 wherein the step of recovering of ammonia from the digestedliquid produces an ammonia fertilizer.
 12. The process of claim 10further comprising the step of recycling water from the digested liquidfollowing ammonia recovery into the remainder.
 13. The process of claim7 further comprising the step of recycling bacteria from said digestedsludge into the remainder.
 14. The process of claim 1 wherein the stepof digesting includes digesting in a tank that includes a plurality ofsectors in series, wherein each sector is portioned from each other. 15.The process of claim 14, wherein the plurality of sectors includes sixsectors in series.
 16. The process of claim 1 wherein said commercialscale of biogas is further defined to include the electricity producedby step (d) being sufficient to provide, after said initial start up ofsaid integrated continuous process, about 75% of the electricity of step(f).
 17. An integrated system for the production of ethanol and selfgenerating energy on a commercial scale after an initial processstart-up, the integrated system comprising: an ethanol facilityproducing commercial scale quantities of ethanol, wherein the productionof commercial scale quantities of ethanol include at least fermentingand distilling to produce commercial scale quantities of ethanol and astillage by-product; an anaerobic digester facility having at least ananaerobic digester, wherein the stillage by-product from the ethanolfacility is included in a mixture digested by the anaerobic digester toproduce commercial scale quantities of biogas and a residue; a generatorfacility for combusting biogas to produce electricity and steam;utilizing steam produced by said generator facility in the ethanolfacility during fermentation and distillation; and utilizing electricityproduced by said generator facility in the ethanol facility duringfermentation, the commercial scale of biogas being defined to include upto 11.6 million BTUs of methane per dry ton of the stillage by-productanaerobically digested with the steam produced being sufficient toprovide, after said initial start up of the process, all the steam usedto produce the ethanol and stillage by-product.
 18. The system of claim17 wherein said commercial scale of biogas is further defined to includethe electricity produced being sufficient to provide, after said initialstart up of the process, about 75% of the electricity duringfermentation.